At the time of purifying methacrylic acid by separating water from a methacrylic acid aqueous solution, a method has been widely known in which methacrylic acid is extracted from the methacrylic acid aqueous solution by an extraction solvent and then methacrylic acid is separated from the extraction solvent. As the extraction solvent to be used in the extraction of methacrylic acid, for example, at least one extracting agent, which can be converted into (meth)acrylic acid, selected from the group consisting of an alkane, alkanol, alkene, and alkenal each having 3 to 4 carbon atoms and methyl tertiary butyl ether (MTBE) is disclosed in Patent Document 1.
Methyl methacrylate or a mixed solvent of methyl methacrylate and n-heptane is disclosed in Patent Document 2.
A mixed solvent containing an aromatic hydrocarbon selected from the group consisting of benzene, toluene, and xylene; and an aliphatic hydrocarbon selected from the group consisting of n-hexane, n-heptane, and n-octane, in which the content of the aromatic hydrocarbon is 20 to 70% by mass, is disclosed in Patent Document 3.    Patent Document 1: Published Japanese Translation No. 2001-514643 of the PCT International Publication    Patent Document 2: Japanese Patent No. 3246216    Patent Document 3: Japanese Patent Application Laid-Open No. 63-211249